This invention relates to an electrode structure of an organic EL display which is constituted by using organic compounds, and which is used for an information display panel, an instrumental panel, or a display for animations or still images in home appliance and electrical components of motor vehicles and motor cycles.
Recently, considerable researches have been done on organic EL devices, and the organic EL devices are about to go into actual use. An organic EL device is a device which has a basic configuration including a transparent electrode (hole injecting electrode) of tin-doped indium oxide (ITO) etc., a thin layer of hole transporting material such as triphenyldiamine (TPD) etc. deposited by evaporation on the transparent electrode, a light emitting layer of a fluorescent material such as aluminum quinolinol complex (Alq3) on the hole transporting layer, and a metal electrode (electron injecting electrode) of a low work function metal such as Mg deposited on the hole transporting layer. Such organic EL devices have drawn public attention for its uses as a display in home appliance and electrical components of motor vehicles and motor cycles since the device is capable of producing a quite high luminance of several hundreds to several 10000 cm/m.sup.2 by the drive voltage of about 10 V.
When a display such as a matrix type display is constituted by using such an organic EL device, wiring of the electrodes comes into question. For example, in FIG. 3 wherein a part of a matrix display is schematically illustrated, an ITO electrode layer 5 corresponding to 1 pixel is deposited on a substrate 1, and a passivation film 6 is deposited to surround the ITO electrode layer 5. An organic layer 7 including a light emitting layer and electron injecting electrode layer 4 are then deposited. Such structure continues to the left direction of FIG. 3 to constitute 1 line of matrix comprising necessary number of pixels. It should be noted that wiring on the side of the hole injecting electrode for connection of the ITO electrode layer 5 is omitted in FIG. 3.
The structure shown in the right-hand part of FIG. 3 is produced by depositing an underlying layer 2 and an electrode layer 3 on the substrate 1 in this order, and a part of the electron injecting electrode layer 4 extends onto the electrode layer 3. The electron injecting electrode layer 4 and the electrode layer 3 are electrically connected at this part. The underlying layer 2 and the electrode layer 3 are connected to terminal electrode (not shown) to the right direction of FIG. 3 to serve the role of power supply line.
When the organic EL display of such structure is produced, a hole injecting electrode structure such as the ITO layer 5 as well as the underlying layer 2 and the electrode layer 3 are first deposited, and the passivation layer 6 and the organic layer 7, and then, the electron injecting electrode layer 4 are deposited.
FIG. 4 is a schematic cross-sectional view of the contacting part (structure shown in the right-hand part of FIG. 3) constituted by the underlying layer 2, the electrode layer 3, and the electron injecting electrode layer 4. As shown in FIG. 4, the electron injecting electrode layer 4 is deposited on the underlying layer 2 and the electrode layer 3 which have been deposited beforehand for contact of the underlying layer 2 and the electrode layer 3 with the electron injecting electrode layer 4. An oxide layer 3a, however, is occasionally formed by oxidation of the surface of the electrode layer 3 during the formation of the passivation layer 6 and the like as shown in FIG. 4. As a consequence, when the electron injecting electrode layer 4 is deposited after the deposition of the organic layer 7, contact between the electrode layer 3 and the electron injecting electrode layer 4 may become insufficient due to the high resistance of the surface portion of the electrode layer 3, and such insufficient contact results in faulty connection and failure in the full drive of the pixels.